linux-kernel - Re: [PATCH 2/2] mm: Make alloc_contig

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Message-ID: <YC0gEBEeeDT1lZhD@dhcp22.suse.cz>
Date:   Wed, 17 Feb 2021 14:54:24 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        David Hildenbrand <david@...hat.com>,
        Muchun Song <songmuchun@...edance.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: Make alloc_contig_range handle in-use hugetlb
 pages

On Wed 17-02-21 14:46:49, Oscar Salvador wrote:
> On Wed, Feb 17, 2021 at 02:36:31PM +0100, Michal Hocko wrote:
> > On Wed 17-02-21 11:08:16, Oscar Salvador wrote:
> > > In-use hugetlb pages can be migrated as any other page (LRU
> > > and Movable), so let alloc_contig_range handle them.
> > > 
> > > All we need is to succesfully isolate such page.
> > 
> > Again, this is missing a problem statement and a justification why we
> > want/need this.
> 
> Heh, I was poor in words.
> 
> "alloc_contig_range() will fail miserably if it finds a HugeTLB page within
>  the range without a chance to handle them. Since HugeTLB pages can be migrated
>  as any other page (LRU and Movable), it does not make sense to bail out.
>  Enable the interface to recognize in-use HugeTLB pages and have a chance
>  to migrate them"
> 
> What about something along those lines?

Is this a real life problem? I know we _can_ but I do not see any
reasoning _why_ should we care all that much.
-- 
Michal Hocko
SUSE Labs